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Show 1905.] MR. R. I. POCIOCK ON A HAINAN GIBBON. 173 It is known that in some species of Gibbons, e. g. II. leuciscus, according to Mr. Hose, the individual variation in colour is considerable, like unto that which obtains indeed in some Squirrels and Lemurs. But, so far as I am aware, it was not previously known that a given individual after reaching maturity may change in colour in the way exemplified by Mr. de St. Croix's specimen. This change may be compared to that which takes place in the hair of the human head concomitantly as a rule with senescence or to that exhibited by some specimens of the Arctic Fox upon the approach of winter*. It is not accompanied by any replacement of coat, nor is it directly attributable to any change in the environment or to external agencies. The cause, whatever it may be, lies within the organism itself; it is constitutional or subjective, and as such may be distinguished by the term " canescence," from the decoloration or fading which is caused by exposure to sunlight or other bleaching agencies. In the case of the Hainan Gibbon it is important to note the coincidence between the appearance of menstruation and that of the colour-change. The former phenomenon began in December 1903, the latter about February 1904. Of the two specimens of this species in the British Museum (both of which are jet-black), one is only about two-thirds grown ; the other, the type, as Mr. Oldfield Thomas states, not quite adult; and since Mr. de St. Croix's specimen is, on the contrary, full-grown, it might be inferred that it is characteristic of the species to change from black to grey upon reaching maturity. This, however, is not the case; for Mr. de St. Croix informs me that he was acquainted in the island of Hainan with another specimen, alleged to be a male, which was jet-black, like his own before coming to the Zoological Gardens, and had been in captivity sufficiently long to justify the belief that it was about twelve years old when he last saw it. Is the canescence, then, a matter of sex and exhibited only by mature females ? The balance of evidence seems to be on the whole in favour of an affirmative reply to this question. For, apart from the change here recorded of the only adult female known, it must be remembered that Mr. Swinhoe, in his published account of all the information respecting the Hainan Gibbon he was able to gather, quotes from the Chinese gazetteer of the Kiung Shan district of the island a passage stating that the male is black and the female white (P. Z. S. 1870, p. 244, &c.). * There are two Arctic Foxes living in the Zoological Gardens at the present time. One remains dark-coated throughout the year; the other turns snow-white towards the winter. In both the winter coat, whether " white " or " blue," is replaced in the summer by a darkish brown clothing of new hair, which is at its best in August, but becomes paler and loses to a large extent its richness of tint as it grows. In neither is there an autumn moult comparable in extent to that of the spring; and there is no doubt that in the animal which turns white the metamorphosis is effected by the destruction of the pigment in the hairs themselves. This bears out Major Barrett-Hamilton's statement as to what occurs in the Arctic Hare. |
